High efficiency resonant circuit



' Aug. 5, 1941.

w. w. HANSEN v HIGH EFFICIENCY RESONANT CIRCUIT Original Filed July 27,1936 3 Sheets-Sheet 1 g- 5, 1941- I w. w. HANSEN I HIGH EFFICIENCYRESQNANT CIRCUIT Original Filed July 27, 1936 INVENTO 1AM W. h mvsENORNEY.

w. w. HANSEN HIGH EFFICIENCY RESONAN'I CIRCUIT Aug. 5, 1941.

3 Sheets-Sheet 3 I INVENTOR (V/LLl/l/Y W HAMSZW,

AZOZN Original Filed July 27, 1936 Patented Au 5, 1941 UNITED STATESPATENT OFFICE REISSUED HIGH EFFICIENCY BESONANI CIRCUIT William W.Hansen, Stanford University, Calif.,

assignor to The Board of Trustees of the Leland Stanford JuniorUniversity, Stanford Univer sity, Oalif., a corporation of CaliforniaOriginal application July 27, 1936, Serial No.

92,787, now Patent No. 2,190,112, dated February 20, 1940.

Divided and this application Jannary 4, 1939, Serial No. 249,194

6 Claims.

The principal object of the present invention is to provide novel meansfor changing the velocity of electrons.

Another object of the present invention lies in the provision of novelcavity resonator or hollow Still another object of the present inventionis to provide means for passing electrons a plurality of times through acavity resonator, each successive passage of the electrons serving tofurther enhance the desired velocity change in the electrons, therebysinusoidally altering the velocitsfiof the electrons at high frequencywhile iiP-iiight and effectively accelerating the elebtrons to highvelocities.

Still another object of this invention is to-provide a novel means andmethod for converting a direct current or low frequency current atrelatively low voltage to high frequency oscillating currents of highvoltage resonant within a hollow resonator and passing electrons throughthe field of said resonator to accelerate the electrons to highvelocities as for use in the production of penetrating X-rays.

Other objects and advantages of this invention will become apparent asthe description proceeds.

This application is a division of my copending application, Serial No.92,787, filed July 27, 1936, Patent No. 2,190,712, dated Feb. 20, 1940for High eiiiciency resonant circuit.

Briefly as to apparatus, my invention comprises a closed conductingshell constituting the inductance and capacitance of a resonant circuit,with one or more generators mounted preferably within the shellconnected to energize the circuit.

In the drawings:

Figure 1 is a partially sectional view of one type of resonator.

Figure 2 is a sectional view taken along line 22 of Figure 1.

Figure 3 is a schematic diagram of the struc ture of Figs. 1 and 2.

Figure 4 shows schematically and graphically the distribution ofpotential and magnetic lines alternative arrangement of the oscillatingresonant circuit of Figures 1 to 3.

Figure 9 is a schematic circuit diagram of my resonant oscillator.

Figure 10 illustrates schematically the use of any resonant oscillatorto produce electrons of extremely high velocities.

Figure 11 is a schematic section taken along line ll-ll of Fig. 10.

Figure 12 illustrates schematically the use of my resonant oscillatorfor the production of X- rays.

The production of electromagnetic oscillations of the order of one meteror less in wave length is diflicult owing to the increased capacitativeand inductive interaction between various circuit leads and elements,the increased effective resistance of the conductors, and a tendency toparasitic radiation from leads and inductance's as the wave length isreduced to the same order of magnitude as the dimensions of variouscircuit elements.

of force in a spherical embodiment of resonator.

Proper shielding and arrangement of parts can overcome in part theinter-lead reactions, but if it is desired to operate several tubes inparallel to secure greater output, these eilects are complicated by theadditional physical handicaps in spacing and arranging the parts, andofier a serious obstacle to satisfactory operation.

The increase in the effective resistance is due to the unsymmetricaldistribution of current in the conductors and inductances. The higherthe frequency, the greater the tendency of the current to travel on thesurface of the conductors; andto crowd to the outer side of inductancewindings, consequently the amount of conducting material actuallyserving is reduced and the effective resistance increased. There is alimit to the gain that may be made by using conductors of larger size,set by the physical limitations of the circuit and the frequencies whichare to be produced.

These obstacles and the tendency toward parasitic radiations may beovercome, however, by utilizing the type of resonant circuit hereinafterdescribed, wherein more stable operation is secured by eliminating theinter-lead reactions, and high efliciency is obtained by eliminatingparasitic radiation and securing an even distribution of current througha large conducting path.

The operation of my invention may be better understood by reference tothe drawings.

In Figurel, I have shown a sectional view of a hollow resonator claimedin application Ser. No.

92,787, wherein a cylindrical shell I, of copper or' other material ofhigh conductivity, is closed by end plates 2 and 4, of similar material,fixed t the cylindrical shell I by bolts or equivalent means. Within theshell I, a cathode plate 8, of diameter substantially less than that ofsaid shell, is supported parallel to the end plates 2 and 4 bysymmetrically placed supporting studs I and 9. Ports I0 and II throughthe shell I permit studs 1 and 9 to pass therethrough without makingcontact with the shell, and to engage insulating blocks I2, fixed toshell I by brackets I4, which serve to supp rt the cathode plate 6 infixed position relative to the shell I. Cathode plate 6 is centrallyperforated by passage I5, and further passages I6 are symmetricallydisposed thereabout.

An anode plate I1 is fixed between and parallel to the ends 2 and 4,soldered or otherwise suitably connected and attached to shell I.Apertures I9 are symmetrically disposed therethrough:

in Figures 1 and 2, these apertures are shown in registry with aperturesI6 through the cathode plate 6. This arrangement is optional, as is theposition of the apertures I6 in the cathode ground plate 6.

In the embodiment of my invention shown in Figures 1 and 2, I have madeuse of one vacuum tube 20 as the oscillation generator; the tube shownis a triode with heater cathode, known to the trade as the acorn type,which is peculiarly adapted by reason of its low internal capacity, lowtransit time, and short, well spaced leads to operation on wavelengthsdown to 0.5 meter. Connection is made to the leads by a special cliptype of terminal. Lead and clip 2| connect the anode to anode plate II.The cathode plate 6 is connected to the cathode terminal by lead 22.Leads 24 and 25 supply current to the heater. The necessary current iscarried into the shell by a twisted pair of wires 26, which connect to apair of fiat copper strips 21 separated from the cathode plate 6 by micaspacers 29; one of the strips 21 is connected to lead 24 and the otherto lead 25. The strips 21 form a radiofrequency by-pass to the cathodeground plate 6. End plate 2 is perforated to permit entrance of gridlead 30, which is centrally positioned by a pair of copper plates 3|fixedly held by bolts 32 relative to end 2, but insulated therefrom bymica sheets 33. The copper plates 3| form a capacitative connectionbetween the grid circuit and the end plate 2 of the shell, althoughconductive connection is prevented by the mica sheets 33. Lead 34connects shell I to an external anode potential source, and lead 35,connected to supporting stud 9, supplies the negative return from thatsource to the cathode.

An aperture 36 may be formed through shell I, and a loop 31 insertedthrough it, for reasons later to be explained. It will be apparent tothose skilled in the art that the acorn tube could be replaced by anyother suitable type of generator capable of producing oscillations ofthe plates may be modifiedgreatly; in some cases a a wire loop issufllcient, and many other modififrequency of the resonant system. Themeans cations in form may be made within the scope of the claims.

Figure 3 shows schematically the connections for operation. A battery 39or other constant potential source ofdirect current is so connected toleads 34 and 35 as to place a positive potential on the anode of tubeZII. An alternating current transformer 40, connected to the twistedpair of leads 26, supplies the heater current. Grid bias is obtainedfrom the drop across a resistor 4I connected between cathode plate 6 andgrid lead 30. Or, tubes may be operated in parallel, and supportedwithin apertures It as in Fig. 10.

A schematic circuit diagram for the embodiment of Figures 1 to 3 isshown in Figure 9.

The closed inductive loop formed by shell I and end plates 2 and 4 iscoupled to the grid by the capacitance between plates 3| and end plate2. The direct current return connection to the oathode is providedthrough a closed inductive loop composed of lead, 30, resistor 4|supplying the grid bias, andthe cathode plate 6. A 0" battery might besubstituted for the resistor H, and be deemed equivalent thereto. Theradio frequency current between cathode and grid through the inductanceloop including plate 6 and shell I is accomplished by the capacitativeconnection between end plate 2 and cathode plate 6. The circuit betweencathode and grid either by way of resistor 4| or by way of shell Iencloses exactly the same lines of force.

Similarly in the anode circuit; the direct conductive path between anodeand cathode links the same lines of force as does the capacitativelycoupled path.

By virtue of the blocking-condenser action of these capacitances, a pathis provided for leading anode and grid potentiafs to the tube withoutpassing through the main inductance, and without setting up circulatingcurrents in the loop formed by the parallel paths, since the same numberof lines of force are enclosed by both.

With the embodiment shown in Figures 1 to 3, as with any closed shell,oscillations may be set up in the circuit at a number of resonantfrequency points but there will be no radiation from the closed shell,in spite of the fact that the physical dimensions may be of the order ofthe wavelengths produced by the frequency of oscillation. That this ispossible may be seen from certain considerations.

Assume that the closed conducting surface within which an oscillatingfield exists, has a thickness large compared with the skin effect depth.

There will then be always in the conductor a depth at which the field Eis vanishingly small. Therefore the Poynting vector also vanishes, andintegrating the Poynting vector over the closed surface it is found thatno energy diverges from the region bounded by the conductor.

The frequency of oscillation within such closed surfaces may becalculated analytically for a few shapes of closures.

It is well known that electro-magnetic fields vary in accord withMaxwells equations, which in free space simplify to A-E=0 A-B=0 1 whereE is the strength of the electric field, B is the strength or themagnetic field, and C 'is a constant.-

These may be changed by standard transformations to the form may beintroduced into Equation 2, which becomes The above equations applystrictly to the conditions in free space. If a conductor is present,Equations I3 must be supplemented by adding terms involving charges andcurrents. In the present case, these terms may be taken into'account byrequiring that E satisfy certain boundary conditions as well as Equation3. Assuming a thin closed surface of infinite conductivity Equation 3must hold inside and outside of the surface, and the tangentialcomponent of E must be zero on that surface.

When Equation 3 is applied to wave motion in free space, any value of Kis possible, but when boundary conditions are imposed, only certaindiscrete values of -K will be compatible with those conditions. Forexample, for any value of l and m, a solution of 'Maxwells equations isE==cos l X cos my sin or t with l'* +m =K and If a cubical shell of zeroresistance and side a is considered, for solutions good inside theshell, the boundary conditions require that, assuming one corner of thecube at the origin,

Ez=0, at 1:0, a and 11:0, 0. (5) To satisfy this limitation, certainvalues of l and m must be used such that where n, n=1, 2, 3 andaccordingly K is fixed, with the frequency This assumes that the shellis a perfect conductor. With a finite resistance, the allowedfrequencies will be shifted slightly, and the oscillations dampedexponentially.

Any closed box will have a set of frequencies at which it may oscillate;for certain simple shapes, analyses similar in general form to thatgiven above for the cube, may be made. For spheres, the analysis may becarried out by the use of functions developed by Mie and Debye; forcylinders, by combination of Bessels functions developed by the inventorand James G. Beckerley; comparable analyses may also be carried out withshapes determined by holding constant various coordinates in any of theseparable systems of Stfickel.

The separable systems of Stackel are orthogonal systems of confocalquadric surfaces. These systems are well known in the" field ofmathematical literature, examples of which are:

(1) Comptes Rendus, vol. 116 (1893) page 485.

(2) Mathematische Annalen, vol. 54 (1901) page 86. e

(3) Mathematische Annalen, vol. 98 (1928) Pa e 749.

(4) Annals of Mathematics, vol. 35 (1934) page (5) Courant-Hilbert,Methoden der Mathematischen Physik I, pages 275-279.

(6) Darboux, "Lecons sur les Systems Orthogonaux et les CoordooneCurviliques especially Livre II, Chap. III, IV, and V.

These mathematical systems, although well known as means for thedelineation of a wide range of geometrical forms, have not heretoforebeen used in the computation of resonant circuits. Inasmuch as acomplete mathematical discussion of the orthogonal systems can be foundin the mathematical literature it is sufficient for present purposes toindicate some simple examples applicable to the computation and designof practical embodiments of this invention.

One convenient system is that described by a pair of hyperbolae ofrevolution intersecting and confocal with -an ellipsoid of revolution.This system develops enclosures that resemble 'a barrel with the endsdented in. The dented ends are hyperbolae confocal with the ellipsoid ofwhich the side of the barrel is a sector. This system may be variedbetween two easily described limits. One limit is that in which the twofoci become cbin'cident and thus become the center of a hollow spherewith reentrant sections of conical shape meeting in the two conicalapexes at the center of the sphere. In other words the barrel side hasbecome '"a sector of a sphere and the dented ends have been formed intocones whose apexes meet at the center of the spherical barrel. The otherlimit is that in which the foci have been separated by an infinitedistance, in which case the sides of the ellipsoid are straight and theintersecting section of the hyperboloids are flat. This produces a rightcircular cylinder as shown in Fig. 1 in which the cylindrical shell I isa section of an ellipsoid and the flat ends land 4 are sections ofhyperboloids.

Similarly the cube is a limiting case of intersecting confocalsuperposed hyperboloids and ellipsoids. The sphere is a special case ofone system.

All the forms of my invention derivable in coordinates of the Stiickelsystems are subject to exact mathematical computation, although some ofthem present considerable practical difliculties in the complete exactsolutions. However, it is entirely feasible to compute a configurationapproximating any practical form ordinarily desired. For example, exactcomputations can be madeeof the properties of the limiting case of thebarrel-shaped form in which the side is spherical and the ends arereentrant cones. Then exact computations can be made of the same form inwhich the foci have been separated so the reentrant hyperbolic barrelends reach well into the barrel but do not touch, for example,one-fourth the way from each end. The two computations then will giveresults between which a practical intermediate form can be estimated.

Obviously the mathematically derived forms will but rarely be theprecise form desired for manufacture. The sharp edges of intersection ofprimarily for convenience in computation. The

practical configuration of the invention may be of any form whatever;For example, the limiting Stackel form of the right circular cylindermay be deformed by making the ends reentrant and of any convenientshape, keeping the sides straight for convenience in manufacture. Bycomputing a series of dimensioned Stackel configurations, it will beimmediately apparent that the electrical properties will vary inaccordance with the dimensions. The following properties are the onesusually considered in resonant circuits: i. e., natural frequency, shuntimpedance, ratio of reactance to resistance, etc. Accordingly, it isobvious that any range of adjustment of any of the properties, can behadby changing the shape of the chamber.

In the case of a sphere, the most simple fields and the lowest frequencyradiations may be .shown to occur with wavelengths of 1.401 and 2.301,where r is the radius of the sphere. These values may be derived fromthe vector wave equations in spherical coordinates, all possiblenoninfinite solutions of which are given by:

A2, 1, M X A (1', 5,1, m) (8) and A3, 1, 1n=KAXA2, l, m where s=J.+./2(Kr) P.- s 0);

and

Letting Equations 8 or 9 represent the field E, the problem is resolvedinto finding K and hence to values which will make the tangentialcomponent vanish at the conducting surface. This involves finding theroots of a certain combination of Bessels functions. There are aninfinite number of such roots, but the simplest one corresponds to onlyone nodal surface for E, at the conducting boundary, and it is this modeof oscillation that would normally be used.

For the function A: of Equation 8, the wavelength is given by therelation )\=l.40r, and oscillations are produced within the sphere inthe mode of Figure 4, wherein the arrows represent the direction andrelative magnitude of the magnetic field B, and the dots represent theelectrostatic field E, lines of which run parallel to the equator. Thegraphs of Figure 4 show the variations of E and B plotted along theequatorial plane against the radius R; with the origin at the Figure 6,with a wavelength i=2.62r and Figure 7 with TTPTQ t m i where r=radiusand H =height of the shell.

In Figure 6, the field-relations are shown for the method of oscillationused in the embodiment of Figures. 1 and 2. The arrows representthedirection and strength of the electric field, and the dots representthe points of greatest intensity of the magnetic field, which runsaround the interior periphery of the shell normal to the elec-' tricfield. The graphs show E and B values against the radius R on thehorizontal midplane of the shell.

In Figure 7 the arrows represent the direction of the magnetic field,and the dots represent the electric field, which runs around the shellhorizontally. The curves are plotted on the horizontalmidplane of thecylindrical shell. The arrangement of the shell and tube for oscillationin the manner of Figure 7 is shown schematically in Figure 8. In thiscase, the dividing partitions are inserted parallel to the axis of thecylindrical container rather than normal thereto. The dotted linesindicate the method of inserting additional tubes for parallel operationto increase the power output. The connecting leads must be kept at rightangles to the electric field, but may be otherwise arranged at will.

.The mode of oscillation may be changed b varying the position andarrangement of the leads and tubes, and since there are an infinitenumber of discrete resonance frequencies possible in a closed container,the tubes and connecting leads may be so inserted as to excite anydesired mode of oscillation.

There is in general a discontinuity of the magnetic field at the innersurface of the conductor,

times and the skin depth increased by V2, so raising the losses by l. or2 The losses are given to order of magnitude in ergs/sec. by P= whereE=field strength in electrostatic volts,

.=wave length in cm. c=vel. of light=3 10 cm. v=conductivity=5.l4 x 10for the copper shell used.

A more useful figure for some purposes is 21- times the ratio of theenergy stored in the electromagnetic field to the energy lost per halfcycle. This number is independent of the field strength and is thequantity which plays the same role for the present type of oscillatingcircuit that plays in ordinary circuits. In fact one easily finds thatLw energy in inductance at peak of cycle -T energy lost per cycle (11-)For any reasonable shape of "resonant circuit of the type hereindescribed the equivalent Q is about for a wavelength of 100 cm.

It should be noted, that since the current distribution is uniform inthe conductor, and the size of the path is much greater than thatavailable by other means, the IR losses are'slightly compared to thosein conventional circuits.

The theoretical discussion given above, properly interpreted,constitutes a mathematical description of my invention as anenergyfield, together with its associated currents and materialboundary. A comparison of the mathematical statement given above, withcorresponding statements applicable to the prior art, will clearlydistinguish my invention from other resonant devices and shieldingarrangements that might be confused with it because of apparent externalresemblances.

Having shown thus that it is possible to produce oscillations at variousdesired resonant frequencies and high efllciencies, various embodimentswill now be described for the useful application of the ultrahigh-frequency currents produced.

If it is desired to utilize the resonant circuit as a power source forradio transmission, an aperture, as 36 in Figure 1, may be made, in theshell i, and a loop 31 inserted to link the fields, thereby producing acurrent in the loop which may be fed directly to an antenna system. Thesize, shape, and position of the loop may be varied in accord with themode of oscillation used.

The fields produced are not only useful in providing circulatingcurrents, but by proper construction, they may be used to accelerateelectrons for various purposes, as shown in Figs, 10 and 11.

These reversals of direction are accomplished by passing the electronsinto the field of magnets It and]: in a direction normal thereto, seeFig. 11, whereupon they are diverted from their paths in .a directionperpendicular to both path and field, and caused to return in theopposite direction. The dimensions of the resonant circuit shell 49 andthe distances between the reversing magnets 5| and 52 are determined bythe frequency of oscillation of the system and the velocity of theelectrons. The distance between magnets BI and 52 should besubstantially that traversed in one-half period of oscillation of thesystem by an electron of velocity corresponding to the voltage by whichit has been accelerated. The intervals spent by the electrons outside ofthe oscillating field, that is, exterior of the chamber, which intervalsare determined by the strength and location of the magnets II and 52,are controllable at will, so that the electrons on all passages throughthe oscillating field will en'- ter in the proper phase relationtocontinue the desired change in velocity. Further. it will be notedthat, while the flight time of the electrons in passing through theresonant chamber is decreasing with each additional passage, it willalso be noted that as the electrons speed up their curved paths at eachreversal of direction becomes larger in diameter and if the electronvelocity is a considerable fraction of the velocity of light, the timespent in making this curved path is increasing, and can be made toproduce a first order compensation of the decrease in'time in the restof the path. Hence, it is possible to In Figure 10, I have shownschematically a cylindrical shell 49 within an airtight envelope 55having suitably apertured cathode and anode plates 6' and i1 therein,and centrally apertured end plates 50, set between two pairs ofelectro-' magnets 5| and 52 arranged to concentrate a magnetic fieldclose to the central axis of and at either end of said cylinder andnormal thereto. Free electrons directed by suitable emitting means 55'into the central portion of shell 49, are accelerated by the electriccomponent of an intense oscillating electromagnetic field built up bythe oscillators 53. The electric component-of this field is most.intense at the center of member 49 and extends from end to end of thismemshell may suffice to give the desired electron velocity. If a greatervelocity is desired, or the accelerating potential is low, the electronmay be caused to reverse its direction of travel each half cycle, andtravel back and forth until the desired velocity is obtained, asindicated schematically by the arrows. If the electrons enter thechamber with an initial velocity of several hundred thousand volts, thevelocity is so large a percentage of the speed of light that furtherenergy additions do not increase the speed markedly since no electroncan exceed the velocity of light, and the electrons may be passed backand forth, gaining energy each half cycle, without getting out of phasewith the oscillating field.

make a number of transits before an appreciable phase error develops. 4

By properly arranging the fields the electrons may be permitted to leavethe accelerating chamber after developing a certain desired velocity,the electrons passing below magnets 52 and being shot into a chamber 54for any desired use.

In Figure 12 I have indicated that an oscillator 50 arranged todevelophigh velocity electrons may be so placed within an envelope 53,as to direct a stream of said electrons upon a suitable anode 46 todevelop X-rays of great penetrating power, for producing X-ray forcancer treatment, or for other desired purposes.

A number of modifications of the embodiments described, all within thescope of the appended claims, will occur to those skilled in the art.

It'is apparent that the envelope 55 shown in Figure 12 may be evacuatedto any desired deand the tube elements may be freely modified andsimplified without regard to conventional limitations resulting from thenecessity of maintaining a vacuum and providing supporting andconnecting leads within a closely associated envelope. It is alsoapparent that I may utilize the oscillating fields within a closedconductin shell to heat inorganic matter, both conducting andnon-conducting, as well as organic-the device then constituting an ultrahigh-frequency induction furnace. It is also apparent that suitablemodifications of my oscillating circuit will permit it to be used as anamplifier.

For a complete understanding of this invention it should be emphasizedthat it is concerned primarily with the delineation of a confinedoscillating electromagnetic field and the transfer of energy into or outof said field. The geometrical a for example.

form of the apparatus and of the electromagnetic field bounded anddelineated thereby is of secondary importance, particularly in view ofthe variety of mechanical shapes of shielded electromagnetic circuitsknown in the prior art. What is important is the mode of oscillation ofthe confined electromagnetic field and the corresponding arrangementsfor sustaining and using said field.

In particulanthree arrangements are used for transferring energy into orout of the confined oscillating field. These are the inductive couplinga large capacitive element might be inoperative loop 31, and thecapacitive coupling plate 6 shown in Fig. 1, and the beam of electronsprojected through the field shown in Fig. 10. The inductive couplingloop 31 is placed in the field so as to interlink a quantity of lines ofmagnetic fiux. The capacitive coupling plate 6 is placed in the fieldwhere it will intercept the desired electric fiux, and the beam ofelectrons of Fig. 10 is projected through the field in a direction andlocation such that the electric field will either accelerate ordecelerate the electrons. Obviously, all of these three arrangements forenergy coupling to the electromagnetic field may be used equally wellfor delivering energy tothe field or for taking energy from the fieldinasmuch as the direction of energy fiow relative to the circuit isdependent merely upon the phase relationship of the several voltages,currents, and fields concerned in the energy transfer.

The inductive loop is effective only to the extent to which itinterlinks magnetic flux of the resonant field. In this connection itwill be noted that conductors are not ordinarily carried entirelythrough the resonant field for couplin The reason for this is evidentfrom Figs, 6 and 7 In Fig. 6 a conductor carried through the center ofthe resonant circular cylinder from top to bottom would, in principle.with its external connections interlink all the magnetic fiux of theenclosed field and the couplingwould apparently be a maximum. I1 theconductor carried through did not lie on the center line. but wereformed into a loop reaching into the ma netic fiux toward either ed e ofthe container the result would be a decrease in the coupling becausesome of the magnetic flux would not be interlinked with the cou lingcircuit with the conse uent cancellation of an amount of flux enuivalentto the flux which is included twice. Thus. for small coeflicients of couling with a conductor carried through the center structure, theconductor must be formed into a large loop with conseouent disadvantagesof distributed capacitance and high resistance. Accordin ly inductivecoupling is made as shown by loop 31 in Fig. 1. In this arrangement thesmaller the loop in general the lesser the coupling.

Further. regarding the conductor carried through the center of anenclosed field of the form shown in Fig. '7. it will be seen that suchan arran ement will have zero coupling inasmuch as the magnetic flux isconfined to regions which are not ma netically interlinked with theconductor. Coupling in a field of this form is, however, madeconveniently by means of a coupling loop as indicated by 31 in Fi l. butrotated 90 degrees from the position shown in Fig. 1. In general. forany mode of oscillation of the confined field a coupling loop 31inserted through the wall of the enclosing surface I as shown in Fig. 1either in the orientation shown or in quadrature therewith willaccomplish ei' fective coupling.

Similarly in the use of capacitive coupling elements, such elements for.maximum effect are comparatively thin plates placed so their flat sur:faces are perpendicular to the electric field lines. In Fig. 6 theproper location for a capacitive coupling element is parallel to thefiat surfaces of the enclosing member I. Such a capacitive element mayhave an-area approximating that of the top or bottom of member I. InFig. 7

because it would short circuit the electric flux in certain regions. Aproper capacitive element would be one comparatively small in comparisonwith the structure as a whole placed in a region in which the electricfiux is in one direction only. Proper locations would be anywhereperpendicular to the circular solid lines representing elec tric fiux inFig. 7.

In coupling an electron beam into the enclosed electromagnetic field asshown in Fig. 10, a condition that should be fulfilled for best resultsis that the electrons should pass through the field in one-half periodof oscillation or less. Effective results are obtained with a time oftransit of the order of a tenth of a period or less. 0bviously, thetransfer of energy between the electrons and the field will take placein any geometrical form of field although for some arrangements it isdesirable to have the field comparatively intense and uniform inthe-region through which the electrons are projected. These conditionsare easily attained using the geometrical delineations ofelectromagnetic field described above in reference to the Stiickelsystems of surfaces. Other desirable forms, however, are obviouslyderivable from the form shown in Fig. 10.

Having described my invention, what I claim and desire to secure byLetters Patent is:

1. Means for producing high electron velocities, comprising asubstantially closed conducting member providing a chamber therein,means for setting up a confined high-frequency standing electromagneticfield within said chamber resonant at the natural frequency of saidmember. means for introducing electrons into said chamber in suchposition that said field will accelerate said electrons during theirpassage through said member, and means for reversing the direction oftravel of said electrons for passage in the reverse direction throughsaid chamber whlle retaining said electrons in proper phasal relationwith said standing field such that the electrons will continue to absorbenergy therefrom. said electrons leaving said chamber when a desiredhigh velocity has been attained.

2. Means for altering the velocity of electrons while in flightcomprising, a hollow internally resonant conducting cavity member, meansfor producing standing electromagnetic waves therein resonant at thenatural frequency of said member, and means for projecting electronssystem of electromagnetic waves is correct for ivin the electrons thedesired acceleration.

4. In a device 01 the character described, a hollow substantially closedconducting member arranged to contain a standing electromagnetic field,means for setting up a standing electromagnetic fleld therein resonantat-the natural frequency of said member, means for projecting a streamof electrons through the fleld for altering the velocity of theelectrons composing the stream, and means for reversing the electronsafter their passage through the field tor eflecting another passage ofthe electrons therethrough to further alter the velocity of theelectrons composing the stream, the field being oi such dimension andsaid reversing means so located with respect thereto. that the electronsreenter the field in the proper phase to effect continued change intheir velocity in the same sense as zliatflobgaining during their firsttransit through e el 5. Means for producing electrons of uniformly highvelocity comprising, an electrical converter, a hollow resonator, meansfor coupling said converter to said resonator for setting up confinedstanding electromagnetic waves therein, and means for passing a streamof electrons through said resonator in the general direction of theelectric component of said waves for effecting passing a stream ofelectrons through said resonator in the general direction of theelectric component of said waves for eflecting changes in the velocityof the electrons of said stream.

WILLIAM W. HANSEN.

